Electric discharge tube



April 23, 1940.

H. BRUINING ET AL ELECTRIC DISCHARGE TUBE Filed March 12, 1938 SECONDARY ELECTRON EMITTER WITH LAYER UFALKAL/NE EARTH METAL OXIDE N0 TH/CKER THAN ONE MICRON AND SUBS TAN TIALL Y FREE OF METAL OF THE OXIDE INVENTORS HAJO BRU/NING AND BY v HENDR/K'DE 305R fl w ATTORNEY.

Patented Apr. 23, 1940 UNITED STATES PATENT OFFIC ELECTRIC DISCHARGE TUBE Hajo Bruining and Jan Hendrik de Boer, Eindhoven, Netherlands, signments, to Radio assignors, by mesne as- Corporation of America,

New York, N. Y., a corporation of Delaware Application March 12,

1938, Serial N0. 195,567

In the Netherlands March 25, 1937 3 Claims.

made to metals and to compounds of alkali metals and alkaline earth metals, metallic caesium absorbed to caesium oxide being very customary.

Applicants have made extensive investigations on this subject and have found that, as regards the value of the secondary emission, it is by no means indifferent whether use is made of compounds or of metals but that a very high secondary emission is only obtained if use is made of an electric. discharge tube according to the present invention which comprises a secondaryemission electrode coated, at least on part of its surface, with a layer which is not thicker than 1 micron and which consists of one or more compounds of the alkali, alkaline earth or earth metals which do practically .not contain free metal. By alkali metals are meant the metals: lithium, sodium, potassium, rubidium and caesium, by alkaline earth metals the metals calcium, strontium, barium and in the present case also magnesium and by the earth metals: aluminium, scandium, yttrium, lanthanum and the rare earth metals, furthermore, zirconium, titanium, hafnium and thorium.

Applicants have found, in fact, that the generally accepted opinion that materials which have a satisfactory primary emission also will have the best secondary emission is incorrect but that the best secondary emission is only obtained it use is made of a layer which consists of one or more compounds in which there is practically no free metal, that is to say of a layer which would be completely unsuitable to act as a primary emitter. Based on this recognition the invention consists in the use of layers which consist or compounds which practically contain no free metal and which have a small thickness, which is necessary as theconductivity of such layers is smaller than that of layers which contain a more or less large amount of free metal.

Although diflerent materials may be utilised for the purpose above referred to, use should preferably be made of oxides, or halogenides of the alkali metals, or alkaline earth metals such, for example, as barium oxide, caesium oxide, sodium chloride, potassium chloride, sodium fluoride, sodium bromide, potassium iodide, aluminium oxide, etc. The table below indicates the values of the secondary emission for the abovementioned compounds and for the pure metals.

Material Sec. emission Voltage As may be seen .from this table the secondary emission of the compounds is materially greater than that of the pure metal.

The accompanying drawing illustrates diagrammatically one embodiment of myinvention as a tube comprising an envelope l enclosing a source of primary electrons, such as a thermionic cathode 2, a conventional control grid 3, an output electrode 4, and a secondary electron emitter 5 constructed in accordance with my invention and. having a layer 6 of alkaline earth oxide on the surface facing the cathode. The primary electron stream fiows, as indicated by a single arrow, from the source 2 to the emitter 5, and the secondary electron stream flows, as indicated by several arrows, from the emitter 5 to the output electrode 4.

What we claim is:

1. An electron discharge tube comprising a source of primary electrons, a collector electrode, and a secondary electron emitting electrode having on the surface exposed to said source a layer no thicker than one micron and consisting of an oxygen compound of a metal selected from the group consisting of the alkali and the alkaline earth metals and substantially. free from the metal of the compound,

2. A secondary electron emitter for an electron discharge device comprising an electrode, and a coating on said electrode thinner than one micron and consisting of an oxide of an alkali or alkaline earth metal and free from the metal of the oxide.

3. A secondary electron emitter for an electron discharge device comprising an electrode, and a coating on said electrode no thicker than one micron and consisting of an oxide of an alkaline earth metal and free from said metal.

HAJO BRUINING. JAN HENDRIK ns BOER. 

